The present disclosure is directed to a sealing device having an intermediate bushing arranged between an outer sleeve and an inner body.
Such sealing devices are particularly used where units are operated with applications involving high fluid pressures (200-4000 bar).
Owing to the extreme operating conditions prevailing there, low-friction gap seals are used for sealing the components that are movable relative to each other, i.e. according to the type disposed between a cylindrical inner body and an outer sleeve, which gap seals have an intermediate bushing which preferably consists of a non-ferrous metal and which is disposed between a wall of a bore of the outer sleeve and the inner body.
In this case, a system-induced leakage is accepted, which leads to a considerable loss of energy however. Thus, in a system-optimized known seal, a leakage quantity of about 600 ml/min is obtained at a fluid pressure of 2000 bar for example and a leakage quantity of about 1200 ml/min at a fluid pressure of 3000 bar. However, this is not conducive to an economically optimized operation of the unit.
This also includes the fact that high leakage leads to wear and tear by erosion of the components involved, resulting in a relatively short service life and the resulting repair and downtime costs.
Such sealing devices are used in this case in assemblies in which the relative movement of the inner sleeve to the outer sleeve takes place axially or in a rotating manner.
The rotating unit can, for example, be designed as a rotary drive for a hydraulic tool. In the case of an electric drive of the rotary drive, the outer sleeve is coupled to a rotor which is operatively connected to a stator, whereas the stationary inner body consists of a sleeve, through which the high-pressure fluid is guided.
This object is achieved by a sealing device having the features of claim 1.
As has been found surprisingly, a sealing device according to the present disclosure leads to a marked reduction in the quantity of leakage, since, unlike a sealing device according to the prior art, almost no operation-related expansion of the annular gap is possible any more.
In a sealing device according to the present disclosure, the fluid under high pressure is fed between the inner body and the intermediate bushing, through the through-openings assigned to the respective chambers, to the corresponding chambers, resulting in a pressure profile in the chambers which follows the pressure profile of the annular gap in a step-like manner. Due to this almost complete compensation between internal and external pressure, a gap expansion is virtually completely prevented. The pressure compensation can be optimized by the number of chambers.
An expansion of the gap between the intermediate bushing and the inner body can be influenced by means of the positioning and division of the chambers as well as of the through-openings, wherein at least one through-opening is associated with each chamber.
Instead of a pressure equalization by the fluid flowing through, the outer pressure can be applied by an external pump by omitting the through-openings, through which a fluid with the corresponding pressure is introduced into the chambers. Typically, this outer pressure corresponds to the internal pressure in the annular gap between the inner body and the intermediate bushing. The outer pressure can be adapted to the internal pressure to be determined by means of a corresponding pump control.
While previously, as mentioned above, the leakage quantity has increased disproportionately with increasing fluid pressure, such a disproportionate increase in the leakage depending on the operating pressure is no longer the case. In other words, the permissible operating pressure is only limited by the component strengths, so that larger nominal widths are possible compared to the known seals.
Compared to the aforementioned leakage quantity according to the prior art, a leakage may now be reduced at an operating pressure of 2000 bar of approximately 90 ml/min and at an operating pressure of 3000 bar approximately the same, namely about 92 ml/min.
In addition to the markedly reduced leakage rate, which allows a significantly improved economic operation of the unit due to the thus reduced energy loss, a sealing device according to the present disclosure also may provide a remarkable increase in the service life of the sealing device, which is due to the reduced load and the resulting lower wear of the involved components.
As experiments have shown, the leakage rate in a prior art sealing device and an operating pressure of 2500 bar increases to 1600 ml/min after about 125 hours, while at a higher operating pressure of 2,800 bar and the same running time of the new sealing device, the leakage rate is approximately 150 ml/min, i.e. only about 9%.
As such, a sealing device according to the present disclosure may provide a significant improvement in the economic operation of a unit provided with a sealing device.
This results, on the one hand, from the mentioned lower energy loss and, on the other hand, from the longer service life, since the components involved must be replaced considerably later than before. This is particularly advantageous when the sealing device is used in an electric rotary drive, since the dismantling and/or mounting work is laborious and thus cost-intensive.